Various embodiments of the invention pertain to navigation systems. More particularly, at least one embodiment of the invention relates to a device, system, and method for dead reckoning navigation for a person on foot.
A pedometer is a device for counting footsteps and has been in use for some time to assist in determining distance traveled by persons on foot. The usefulness of a pedometer depends on knowing the length of each footstep, or the xe2x80x9cstridexe2x80x9d, and the assumption that the direction of travel is straight ahead. A person""s walk or stride typically varies in response to a number of circumstances, including, but not limited to, walking sideways or backwards, and going uphill or downhill. Stride changes even more drastically if a person runs instead of walks.
If a pedometer is used in conjunction with a device to determine direction of travel, such as a magnetic compass, navigation by dead reckoning is possible. For example, the system described in U.S. Pat. No. 5,583,776 uses stride data from a pedometer combined with compass data. However, that device does not compensate for non-forward walking motions.
Dead reckoning permits knowing the user""s location with respect to some known reference, such as his starting point. When determining position of the user by dead reckoning techniques, unusual walking motions introduce errors if a person steps sideways or backwards as, for example, a soldier may need to do to evade an enemy or obstacle. In these cases, the direction of travel may differ from the direction the user is facing, which is the direction that would be reported by a compass attached to the person""s torso.
Thus, prior art dead reckoning systems typically fail to accurately account for non-forward walking motions and changes in stride length.
U.S. Pat. Nos. 6,305,221 and 6,301,964 describe dead reckoning navigations systems and methods in which accelerometers are mounted on the user""s foot or leg. It is theoretically possible to measure a user""s motion directly by double integration of acceleration with time, but currently available accelerometers severely limit the accuracy of this method when the accelerometers are mounted on or near a user""s waist. Where the information to be integrated is much smaller than gravity, typical accelerometer components are distorted by gait rotations and other sources of noise. This is the reason prior art dead reckoning navigation systems specify mounting the accelerometers on a user""s foot or extremities, where the acceleration magnitudes are greater.
However, mounting the accelerometers around a user""s foot or extremities, and the need to communicate results from the accelerometers by wire or radio transmission methods, is subject to other sources of error, is less convenient, potentially more expensive and sometimes impractical.